1. Field of the Invention
The present invention relates to an apparatus and method for controlling lighting brightness through digital conversion.
2. Description of the Related Art
In general, lightings serve to brighten a dark place such that people can recognize something. As for the lightings, light emitting diodes (LEDs), fluorescent lamps, incandescent lamps and so on are usually used.
The brightness and color of lightings can be controlled in accordance with the magnitude of a driving voltage. In this case, the duty width of a PWM (Pulse Width Modulation) signal is adjusted to control the brightness and color.
Hereinafter, a conventional apparatus for controlling lighting brightness will be described with reference to FIGS. 1 and 2.
FIG. 1 is a block diagram of a conventional apparatus for controlling lighting brightness. FIG. 2 is a diagram for explaining a process of controlling the duty width of a PWM signal.
As shown in FIG. 1, the conventional apparatus for controlling lighting brightness includes a lighting control unit 110, a PWM signal generating unit 120, a driving voltage generating unit 130, and a lighting unit 140.
The lighting control unit 110 is connected to the PWM signal generating unit 120 and generates a control signal S for controlling the brightness and color of first to nth lightings 140a to 140n provided in the lighting unit 140.
The lighting control unit 110 receives a current flowing in each lighting of the lighting unit 140 and compares the current with a preset reference value. When the received current is smaller than the reference value, the lighting control unit 110 generates a control signal S for increasing the magnitude of a driving voltage Vc. When the received current is larger than the reference value, the lighting control unit 110 generates a control signal S for reducing the magnitude of a driving voltage Vc.
The PWM signal generating unit 120 is composed of first to nth PWM signal generating sections 120a to 120n. The first to nth PWM signal generating sections 120a to 120n are controlled by the control signal S to generate PWM signals P for increasing or reducing the magnitude of the driving voltage Vc.
At this time, when the control signal S is a signal for reducing the magnitude of the driving voltage Vc, the first to nth PWM signal generating sections 120a to 120n reduce the width of a duty-on interval of the PWM signals P and then output the PWM signals P. Further, when the control signal S is a signal for increasing the magnitude of the driving voltage Vc, the first nth PWM signal generating sections 120a to 120n increase the width of the duty-on interval of the PWM signals P and then output the PWM signals P.
Then, the first to nth driving voltage generating sections 130a to 130n of the driving voltage generating unit 130 receive the PWM signals P of which the duty width is controlled and then output driving voltages Vc corresponding to the PWM signals P, thereby controlling the brightness of the first to nth lightings 140a to 140n. 
However, the apparatus for controlling lighting brightness has the following problems.
The apparatus generates the PWM signals P with a constant period to drive the first to nth lightings 140a to 140n. At this time, the width of the duty-on interval of the PWM signals P is increased or reduced by the control signal S to control the driving voltages Vc. However, since the PWM signals P have a constant period, a spurious signal is generated.
Further, because of the spurious signal generated when the plurality of lightings 140a to 140n are driven, noise occurs in the apparatus. Then, lighting efficiency decreases.